As is well known, in all cameras, the film must be positioned in the focal plane of the optical system and, in the roll-film type camera, the film must be wound from one spool, or reel, to another to permit a series of pictures to be made on the roll of film.
Problems have arisen in the past in cameras, and especially in X-ray cameras, when relatively large and heavy film is used, and where high speed transport of the film from frame-to-frame is desired. This is because, as the weight of the film increases, its inertia increases with a power of 2. With large size, heavy films, therefore, any abrupt start or stops of the film creates shocks in the film and adversely affects the images developed thereon. However, it is necessary that the film be completely stopped at each successive frame for each successive exposure, and when high speeds are required, the aforesaid problem arises.
As described briefly above, the problem is solved in the drive mechanism of the present invention by the provision of a lost motion drive mechanism which causes the drive motor to impart a varying speed to the transport. For example, as the drive motor rotates through 0.degree.-180.degree., the transport is accelerated so that its speed rises from zero to a maximum at 180.degree.; and as the drive motor rotates through 180.degree.-360.degree., the transport is decelerated so that its speed drops from a maximum of zero at 360.degree.. As also described, a unique self-tightening clutch assembly is also provided to produce one revolution only of the drive shaft of the camera each time the mechanism is activated.
In this way, the lost motion drive mechanism of the invention overcomes inertia problems in either starting or stopping a mass, such as an X-ray film. In a particular constructed embodiment of the invention, for example, in which the drive mechanism was used to drive X-ray film in an X-ray camera, the drive motor was caused to rotate four times faster than the transport for the first and last 5.degree. of angular movement of the motor, whereas at the center of the cycle, the transport is caused to travel 1.75 times faster than the drive motor.